The present invention relates to a voltage control apparatus for a vehicle generator wherein an ignition switch and a charge lamp are connected in series so that a single input terminal is commonly used for these elements.
As a voltage control apparatus for a vehicle generator which has an input terminal for inputting a battery voltage through an ignition switch and a charge lamp and starts the operation when the voltage at the input terminal exceeds a predetermined value, there is known one disclosed in Japanese Patent No. 2707616. FIG. 6 shows a circuit diagram of the voltage control apparatus disclosed in the Japanese Patent.
The voltage control apparatus 1 shown in FIG. 6 is arranged in a manner that the voltage control apparatus includes an input terminal L for inputting the voltage of a battery 5 through an ignition switch 3 and a charge lamp 4 connected in series with the ignition lamp and starts the excitation of a rotary coil 21 of a vehicle generator 2 when the voltage at the input terminal L exceeds a predetermined value. The voltage control apparatus 1 further includes a comparison means 12 which generates an output signal when the voltage at the input terminal L exceeds another predetermined value lower than the aforesaid predetermined value, and a switch means 14 which operates in response to the output signal thereby to connect a leak compensation resistor 143 between the input terminal L and the ground.
To be more concrete, the voltage control apparatus 1 shown in FIG. 6 includes comparators 12, 13. The voltage of the input terminal L is applied to each of the negative “−” terminals of these comparators. Constant voltages V1, V2 are applied to the positive “+”, terminals of the comparators 12, 13, respectively, wherein V1<V2. A transistor 16 is connected to the output terminal of the comparator 12. A transistor 14 serving as a switch means is turned on in response to the output of the transistor 16 applied through a resistor 142. A transistor 1112 is connected to the output terminal of the comparator 13. A power transistor 11 is turned on in response to the output of the transistor 1112 applied through a resistor 1114.
The transistor 14 and a transistor 152 are connected to a comparator 15 through transistors 141, 151, respectively. When the vehicle generator 2 starts the electric power generation operation, the voltage generated by the generator exceeds a constant voltage V3, so that the comparator 15 turns off the transistors 14, 152. In the figure, reference numerals 22, 23 depict the stator coil and the full-wave rectifier of the vehicle generator 2 respectively. A resistor 144 provided between the input terminal L and the ground serves to lower the voltage at the input terminal L to the ground level upon the normal opening operation of the ignition switch 3.
During the electric power generation operation, the power transistor 11 is turned on and off in response to a transistor 1111. A zener diode 1113 is provided on the base side of the transistor 1111.
An example of the conventional voltage control apparatus for a vehicle generator is shown in FIG. 7 in which a light emitting element such as a light emitting diode driven with a low dissipation power is employed as the charge lamp. When the light emitting diode etc. is employed as the charge lamp as shown in FIG. 7, it is required to mount a current limit resistor in series with the light emitting diode etc. on a vehicle side in order to prevent the occurrence of such a phenomenon that a transistor 152 for turning on the light emitting diode etc. is broken by an overcurrent.
However, when the current limit resistor is mounted on the vehicle side, the arrangement of the apparatus on the vehicle side becomes complicated. Further, even in the case where the current limit resistor is inserted on the vehicle side, there arises a problem that, when a high voltage such as a battery voltage etc. is directly applied to the input terminal L due to the abnormality of the vehicle wiring etc., the transistor for driving the light emitting element (light emitting diode etc.) driven with a low dissipation power may be broken by an overcurrent.
Further, there is a problem that a dedicated element such as a transistor etc. for lightening the light emitting element is required and that the light emitting element may always be kept in a lightened state by a current flowing into the input terminal L for starting the operation of the voltage control apparatus.